Eocene Thermal Maximum 2

Short description: Transient period of global warming that occurred approximately 54 million years ago

Eocene Thermal Maximum 2 (ETM-2), also called H-1 or Elmo (Eocene Layer of Mysterious Origin), was a transient period of global warming that occurred around 54 Ma. It was the second major hyperthermal that punctuated long-term warming from the Late Paleocene through the Early Eocene (58 to 50 Ma).

## Contents

* 1 Timing
* 2 Causes
* 3 Effects
* 4 See also
* 5 References
* 6 External links

## Timing

ETM-2 occurred exactly 4.5 long eccentricity cycles after the PETM.[1] ETM-2 is clearly recognized in sediment sequences by analyzing the stable carbon isotope composition of carbon-bearing material.[2][3][4] The 13C/12C ratio of calcium carbonate or organic matter drops significantly across the event.[5][6] This is similar to what happens when one examines sediment across the PETM, although the magnitude of the negative carbon isotope excursion is not as large during ETM-2. The timing of Earth system perturbations during ETM-2 and PETM also appear different. Specifically, the onset of ETM-2 may have been longer (perhaps 30,000 years) while the recovery seems to have been shorter (perhaps <50,000 years). However, these findings are caveated by the fact that the timing of short-term carbon cycle perturbations during both events remains difficult to constrain.[7]

A thin clay-rich horizon marks ETM-2 in marine sediment from widely separated locations. In sections recovered from the deep sea (for example those recovered by Ocean Drilling Program Leg 208 on Walvis Ridge), this layer is caused by dissolution of calcium carbonate.[7] However, in sections deposited along continental margins (for example those now exposed along the Waiau Toa / Clarence River, New Zealand), the clay-rich horizon represents dilution by excess accumulation of terrestrial material entering the ocean. Similar changes in sediment accumulation are found across the PETM.[8] In sediment from Lomonosov Ridge in the Arctic Ocean, intervals across both ETM-2 and PETM show signs of higher temperature, lower salinity and lower dissolved oxygen.[9]

## Causes

The PETM and ETM-2 are thought to have a similar generic origin, although this idea remains at the edge of current research. Both events were geologically brief time intervals (<200,000 years), and during both events, a tremendous amount of 13C-depleted carbon rapidly entered the ocean and atmosphere.[10] This decreased the 13C/12C ratio of carbon-bearing sedimentary components, and dissolved carbonate in the deep ocean. The source of this 13C-depleted carbon during ETM-2 is believed to be organic carbon.[11] Somehow carbon input was coupled to an increase in Earth surface temperature and a greater seasonality in precipitation, which explains excess terrestrial sediment discharge marking both events in continental margin sections. Explanations for changes during ETM-2 are the same as those for the PETM, and are discussed in that article.

Both the PETM and ETM-2 occurred during maxima in the short eccentricity cycle, suggesting that the events may have had to do with this Milankovitch cycle. However, the PETM followed a long eccentricity minimum while ETM-2 followed a long eccentricity maximum, indicating a qualitative difference in the orbital causes of these two events.[1] The H-2 event appears to be a "minor" hyperthermal that follows ETM-2 (H-1) by about 100,000 years. This has led to speculation that the two events are somehow coupled and paced by changes in orbital eccentricity.[8][7]

## Effects

ETM-2 and the other hyperthermals Early Eocene hyperthermals occurring in close temporal proximity appear to have ushered in the Early Eocene Climatic Optimum (EECO), the warmest sustained interval of the Cenozoic Era.[12]

Continental silicate weathering increased by 18-22% during ETM-2 according to marine 187Os/188Os measurements, retarding some of the carbon-driven warming.[13] Unlike during the PETM, the increases in precipitation during ETM-2 were too insignificant to buffer the global warming in any substantial way.[14]

Sea surface temperatures (SSTs) in the Arctic Ocean rose by 3–5 °C during ETM-2.[9] SSTs climbed by 2–4 °C and salinity by ~1–2 ppt[clarification needed] in subtropical waters.[15] Deep sea temperatures in the South Atlantic rose to 16.9 ± 2.3 °C from a background of 13.5 ± 1.9 °C.[16] On land, precipitation in the Arctic around Stenkul Fjord increased,[17] enhancing clastic sedimentation.[18] Surface temperatures in the Fushun Basin rose by 3–5 °C while mean annual precipitation (MAP) rose by 600 mm.[19] At the Equator, precipitation decreased, leading to a severe decline in tropical rainforests and an expansion of deciduous forests in their place.[20]

Ocean acidification did occur during ETM-2,[21] just as it did in the PETM, but the magnitude of the drop in pH was significantly lower.[22] Along the Atlantic Coastal Plain, changes in local hydrology and nutrient supply were minimal, unlike during the PETM.[23] In the Tethys Ocean, an increase in surface water eutrophication is recorded.[24]

Anoxia was absent during ETM-2, as the magnitude of the hyperthermal was not sufficient to generate large scale marine anoxia.[25] However, oxygen levels in many regions of the world's oceans did decline.[26]

The marine ecological recovery from the PETM was significantly inhibited by ETM-2.[27] As in the case of the PETM, reversible dwarfing of mammals has been noted to have occurred during the ETM-2.[28][29] Unlike during the PETM, there was no change in the photosymbiont associations of the planktonic foraminifer Acarinina soldadoensis, possibly because the PETM had already selected for adaptations enabling them to withstand extreme hyperthermals or because of the lesser magnitude of ETM-2.[30] In the Tethys, planktonic foraminifer test size decreased by 40%, while calcareous nannoplankton community sizes dropped as reflected by increased abundance of small placoliths.[31] In the benthic realm, the fauna came under a high degree of stress due to dysoxic conditions.[26]

## See also

* Latest Danian Event
* Paleocene–Eocene Thermal Maximum
* Eocene Thermal Maximum 3

## References

1. ↑ 1.0 1.1 Westerhold, Thomas; Röhl, Ursula; Laskar, Jacques; Raffi, Isabella; Bowles, Julie; Laurens, Lucas J.; Zachos, James C. (6 April 2007). "On the duration of magnetochrons C24r and C25n and the timing of early Eocene global warming events: Implications from the Ocean Drilling Program Leg 208 Walvis Ridge depth transect". Paleoceanography and Paleoclimatology 22 (2). doi:10.1029/2006PA001322. Bibcode: 2007PalOc..22.2201W.
2. ↑ Lourens, L.J.; Sluijs, A.; Kroon, D.; Zachos, J.C.; Thomas, E.; Röhl, U.; Bowles, J.; Raffi, I. (2005). "Astronomical pacing of late Palaeocene to early Eocene global warming events". Nature 435 (7045): 1083–1087. doi:10.1038/nature03814. PMID 15944716. Bibcode: 2005Natur.435.1083L.
3. ↑ Slotnick, B.S.; Dickens. G.R.; Nicolo, M.J.; Hollis, C.J.; Crampton, J.S.; Zachos, J.C.; Sluijs, A. (2012). "Large amplitude variations in carbon cycling and terrestrial weathering during the latest Paleocene and earliest Eocene: The record at Mead Stream, New Zealand". Journal of Geology 120 (5): 487–505. doi:10.1086/666743. Bibcode: 2012JG....120..487S.
4. ↑ Abels, H.A..; Clyde, H.C.; Gingerich, P.D.; Hilgen, F.J.; Fricke, H.C.; Bowen, G.J.; Lourens, L.J. (2012). "Terrestrial carbon isotope excursions and biotic change during Palaeogene hyperthermals". Nature Geoscience 5 (8): 326–329. doi:10.1038/NGEO1427. Bibcode: 2012NatGe...5..326A.
5. ↑ Clementz, Mark; Bajpai, S.; Ravikant, V.; Thewissen, J. G. M.; Saravanan, N.; Singh, I. B.; Prasad, V. (1 January 2011). "Early Eocene warming events and the timing of terrestrial faunal exchange between India and Asia". Geology 39 (1): 15–18. doi:10.1130/G31585.1. Bibcode: 2011Geo....39...15C. https://pubs.geoscienceworld.org/gsa/geology/article-abstract/39/1/15/130365/Early-Eocene-warming-events-and-the-timing-of. Retrieved 6 April 2023.
6. ↑ Galeotti, Simone; Sprovieri, Mario; Rio, Domenico; Moretti, Matteo; Francescone, Federica; Sabatino, Nadia; Fornaciari, Eliana; Giusberti, Luca et al. (1 August 2019). "Stratigraphy of early to middle Eocene hyperthermals from Possagno (Southern Alps, Italy) and comparison with global carbon isotope records". Palaeogeography, Palaeoclimatology, Palaeoecology 527: 39–52. doi:10.1016/j.palaeo.2019.04.027. Bibcode: 2019PPP...527...39G. https://www.sciencedirect.com/science/article/abs/pii/S0031018218310307. Retrieved 4 December 2022.
7. ↑ 7.0 7.1 7.2 Stap, L.; Lourens, L.J.; Thomas, E.; Sluijs, A.; Bohaty, S.; Zachos, J.C. (2010). "High-resolution deep-sea carbon and oxygen isotope records of Eocene Thermal Maximum 2 and H2". Geology 38 (7): 607–610. doi:10.1130/G30777.1. Bibcode: 2010Geo....38..607S. http://geology.geoscienceworld.org/cgi/content/abstract/38/7/607.
8. ↑ 8.0 8.1 Nicolo, M.J.; Dickens, G.R.; Hollis, C.J.; Zachos, J.C. (2007). "Multiple early Eocene hyperthermals: Their sedimentary expression on the New Zealand continental margin and in the deep sea". Geology 35 (8): 699–702. doi:10.1130/G23648A.1. Bibcode: 2007Geo....35..699N. http://geology.geoscienceworld.org/cgi/content/abstract/35/8/699.
9. ↑ 9.0 9.1 Sluijs, A.; Schouten, S.; Donders, T.H.; Schoon. P.L.; Röhl, U.; Reichart, G.-J.; Sangiorgi, F.; Kim, J.-H. et al. (2009). "Warm and wet conditions in the Arctic region during Eocene Thermal Maximum 2". Nature Geoscience 2 (11): 777–780. doi:10.1038/ngeo668. Bibcode: 2009NatGe...2..777S.
10. ↑ Zachos, J.C.; Dickens, G.R.; Zeebe, R.E. (2008). "An early Cenozoic perspective on greenhouse warming and carbon-cycle dynamics". Nature 451 (7176): 279–283. doi:10.1038/nature06588. PMID 18202643. Bibcode: 2008Natur.451..279Z.
11. ↑ Harper, Dustin T.; Hönisch, Bärbel; Bowen, Gabriel J.; Zeebe, Richard E.; Haynes, Laura L.; Penman, Donald E.; Zachos, James C. (3 September 2024). "Long- and short-term coupling of sea surface temperature and atmospheric CO 2 during the late Paleocene and early Eocene" (in en). Proceedings of the National Academy of Sciences of the United States of America 121 (36). doi:10.1073/pnas.2318779121. ISSN 0027-8424. PMID 39186648.
12. ↑ Slotnick, B. S.; Dickens, G. R.; Hollis, C. J.; Crampton, J. S.; Strong, C. Percy; Phillips, A. (17 September 2015). "The onset of the Early Eocene Climatic Optimum at Branch Stream, Clarence River valley, New Zealand". New Zealand Journal of Geology and Geophysics 58 (3): 262–280. doi:10.1080/00288306.2015.1063514. Bibcode: 2015NZJGG..58..262S.
13. ↑ Tanaka, Erika; Yasukawa, Kazutaka; Ohta, Junichiro; Kato, Yasuhiro (15 August 2022). "Enhanced continental chemical weathering during the multiple early Eocene hyperthermals: New constraints from the southern Indian Ocean" (in en). Geochimica et Cosmochimica Acta 331: 192–211. doi:10.1016/j.gca.2022.05.022. https://www.sciencedirect.com/science/article/pii/S0016703722002654. Retrieved 11 March 2025.
14. ↑ Samanta, Arpita; Bera, Melinda Kumar; Bera, Subir; Longstaffe, Fred J.; Paul, Shubhabrata; Kumar, Kishor; Sarkar, Anindya (December 2024). "The temperature-precipitation duel and tropical greening during the Early Eocene Greenhouse episode" (in en). Global and Planetary Change 243. doi:10.1016/j.gloplacha.2024.104603. https://www.sciencedirect.com/science/article/pii/S0921818124002509. Retrieved 11 March 2025.
15. ↑ Harper, Dustin T.; Zeebe, Richard; Hönisch, Bärbel; Schrader, Cindy D.; Lourens, Lucas J.; Zachos, James C. (20 December 2017). "Subtropical sea-surface warming and increased salinity during Eocene Thermal Maximum 2". Geology 46 (2): 187–190. doi:10.1130/G39658.1. https://pubs.geoscienceworld.org/gsa/geology/article-abstract/46/2/187/525529/Subtropical-sea-surface-warming-and-increased?redirectedFrom=fulltext. Retrieved 25 June 2023.
16. ↑ Agterhuis, Tobias; Ziegler, Martin; de Winter, Niels J.; Lourens, Lucas J. (24 February 2022). "Warm deep-sea temperatures across Eocene Thermal Maximum 2 from clumped isotope thermometry" (in en). Communications Earth & Environment 3 (1): 1–9. doi:10.1038/s43247-022-00350-8. ISSN 2662-4435. https://www.nature.com/articles/s43247-022-00350-8. Retrieved 11 March 2025.
17. ↑ Blumenberg, Martin; Naafs, B. David A.; Lückge, Andreas; Lauretano, Vittoria; Schefuß, Enno; Galloway, Jennifer M.; Scheeder, Georg; Reinhardt, Lutz (30 January 2024). "Biomarker Reconstruction of a High‐Latitude Late Paleocene to Early Eocene Coal Swamp Environment Across the PETM and ETM‐2 (Ellesmere Island, Arctic Canada)" (in en). Paleoceanography and Paleoclimatology 39 (2). doi:10.1029/2023PA004712. ISSN 2572-4517. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2023PA004712. Retrieved 11 March 2025.
18. ↑ Reinhardt, Lutz; von Gosen, Werner; Lückge, Andreas; Blumenberg, Martin; Galloway, Jennifer M.; West, Christopher K.; Sudermann, Markus; Dolezych, Martina (1 February 2022). "Geochemical indications for the Paleocene-Eocene Thermal Maximum (PETM) and Eocene Thermal Maximum 2 (ETM-2) hyperthermals in terrestrial sediments of the Canadian Arctic" (in en). Geosphere 18 (1): 327–349. doi:10.1130/GES02398.1. ISSN 1553-040X. https://pubs.geoscienceworld.org/gsa/geosphere/article/18/1/327/610709/Geochemical-indications-for-the-Paleocene-Eocene. Retrieved 11 March 2025.
19. ↑ Li, Yuanji; Sun, Pingchang; Falcon-Lang, Howard J.; Liu, Zhaojun; Zhang, Baoyong; Zhang, Qiang; Wang, Junxian; Xu, Yinbo (15 January 2023). "Eocene hyperthermal events drove episodes of vegetation turnover in the Fushun Basin, northeast China: Evidence from a palaeoclimate analysis of palynological assemblages". Palaeogeography, Palaeoclimatology, Palaeoecology 610. doi:10.1016/j.palaeo.2022.111317. Bibcode: 2023PPP...61011317L. https://www.sciencedirect.com/science/article/abs/pii/S0031018222004886. Retrieved 3 December 2022.
20. ↑ Srivastava, Gaurav; Bhatia, Harshita; Verma, Poonam; Singh, Yogesh P.; Agrawal, Shailesh; Utescher, Torsten; Mehrotra, R. C. (September 2024). "A transient shift in equatorial hydrology and vegetation during the Eocene Thermal Maximum 2" (in en). Geoscience Frontiers 15 (5). doi:10.1016/j.gsf.2024.101838. https://www.sciencedirect.com/science/article/pii/S1674987124000628. Retrieved 11 March 2025.
21. ↑ Jiang, Shijun; Cui, Ying; Wang, Yasu (March 2021). "Carbon cycle variability in tropical Atlantic across two Early Eocene hyperthermals" (in en). Geoscience Frontiers 12 (2): 521–530. doi:10.1016/j.gsf.2020.07.014. https://www.sciencedirect.com/science/article/pii/S1674987120301791. Retrieved 11 March 2025.
22. ↑ Harper, D. T.; Hönisch, B.; Zeebe, R. E.; Shaffer, G.; Haynes, L. L.; Thomas, E.; Zachos, James C. (18 December 2019). "The Magnitude of Surface Ocean Acidification and Carbon Release During Eocene Thermal Maximum 2 (ETM-2) and the Paleocene-Eocene Thermal Maximum (PETM)" (in en). Paleoceanography and Paleoclimatology 35 (2). doi:10.1029/2019PA003699. ISSN 2572-4517. https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2019PA003699. Retrieved 31 December 2023.
23. ↑ Rush, William; Self-Trail, Jean; Zhang, Yang; Sluijs, Appy; Brinkhuis, Henk; Zachos, James; Ogg, James G.; Robinson, Marci (17 August 2023). "Assessing environmental change associated with early Eocene hyperthermals in the Atlantic Coastal Plain, USA" (in en). Climate of the Past 19 (8): 1677–1698. doi:10.5194/cp-19-1677-2023. ISSN 1814-9332. Bibcode: 2023CliPa..19.1677R. https://cp.copernicus.org/articles/19/1677/2023/. Retrieved 1 November 2024.
24. ↑ D'Onofrio, Roberta; Luciani, Valeria; Fornaciari, Eliana; Giusberti, Luca; Boscolo Galazzo, Flavia; Dallanave, Edoardo; Westerhold, Thomas; Sprovieri, Mario et al. (24 August 2016). "Environmental perturbations at the early Eocene ETM2, H2, and I1 events as inferred by Tethyan calcareous plankton (Terche section, northeastern Italy)" (in en). Paleoceanography and Paleoclimatology 31 (9): 1225–1247. doi:10.1002/2016PA002940. ISSN 0883-8305. Bibcode: 2016PalOc..31.1225D. https://agupubs.onlinelibrary.wiley.com/doi/10.1002/2016PA002940. Retrieved 1 November 2024.
25. ↑ Stassen, Peter; Steurbaut, Etienne; Morsi, Abdel-Mohsen M.; Schulte, Peter; Speijer, Robert P. (January 2012). "Biotic impact of Eocene thermal maximum 2 in a shelf setting (Dababiya, Egypt)". Austrian Journal of Earth Sciences 105 (1): 154-160. https://www.researchgate.net/publication/236610150_Biotic_impact_of_Eocene_thermal_maximum_2_in_a_shelf_setting_Dababiya_Egypt. Retrieved 11 March 2025.
26. ↑ 26.0 26.1 Das, Mohuli; Dasgupta, Sudipta; Roy Choudhury, Tathagata; D'Souza, Renzo; Banerjee, Santanu (1 April 2024). "Impact of early Eocene (Ypresian) warming events on ichnological assemblage of the Naredi Formation, western Kutch (Kachchh) Basin of Gujarat, India" (in en). Palaeogeography, Palaeoclimatology, Palaeoecology 639. doi:10.1016/j.palaeo.2024.112063. https://www.sciencedirect.com/science/article/pii/S003101822400052X. Retrieved 11 March 2025.
27. ↑ Arreguín-Rodríguez, Gabriela J.; Thomas, Ellen; D'haenens, Simon; Speijer, Robert P.; Alegret, Laia (23 February 2018). Frontalini, Fabrizio. ed. "Early Eocene deep-sea benthic foraminiferal faunas: Recovery from the Paleocene Eocene Thermal Maximum extinction in a greenhouse world" (in en). PLOS ONE 13 (2). doi:10.1371/journal.pone.0193167. ISSN 1932-6203. PMID 29474429. Bibcode: 2018PLoSO..1393167A.
28. ↑ D'Ambrosia, Abigail R.; Clyde, William C.; Fricke, Henry C.; Gingerich, Philip D.; Abels, Hemmo A. (15 March 2017). "Repetitive mammalian dwarfing during ancient greenhouse warming events". Science Advances 3 (3). doi:10.1126/sciadv.1601430. PMID 28345031. Bibcode: 2017SciA....3E1430D.
29. ↑ Erickson, J. (2013-11-01). "Global warming led to dwarfism in mammals – twice". University of Michigan. http://www.ns.umich.edu/new/releases/21789-global-warming-led-to-dwarfism-in-mammals-twice.
30. ↑ Davis, Catherine V.; Shaw, Jack O.; D'haenens, Simon; Thomas, Ellen; Hull, Pincelli M. (26 September 2022). Incarbona, Alessandro. ed. "Photosymbiont associations persisted in planktic foraminifera during early Eocene hyperthermals at Shatsky Rise (Pacific Ocean)" (in en). PLOS ONE 17 (9). doi:10.1371/journal.pone.0267636. ISSN 1932-6203. PMID 36155636. Bibcode: 2022PLoSO..1767636D.
31. ↑ D'Onofrio, R.; Barrett, R.; Schmidt, D. N.; Fornaciari, E.; Giusberti, L.; Frijia, G.; Adatte, T.; Sabatino, N. et al. (7 June 2024). "Extreme Planktic Foraminiferal Dwarfism Across the ETM2 in the Tethys Realm in Response to Warming" (in en). Paleoceanography and Paleoclimatology 39 (6). doi:10.1029/2023PA004762. ISSN 2572-4517. Bibcode: 2024PaPa...39.4762D. https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2023PA004762. Retrieved 1 November 2024.

## External links

* Appy Sluijs. "Climate and carbon cycle dynamics during late Paleocene – early Eocene transient global warming events". http://ftp.nioz.nl/public/colloquia/appysluijs.pdf.
* "Patterns and magnitude of deep sea carbonate dissolution during Eocene Thermal Maximum 2 and H2, Walvis Ridge, southeastern Atlantic Ocean". http://www.agu.org/pubs/crossref/2009/2008PA001655.shtml.

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